Eldest

A name for the oldest of beings

A title used of two immensely ancient beings in Middle-earth: Tom Bombadil and Treebeard the Ent. At the end of the Third Age, both of these had lived in the World for many millennia, though by Bombadil's own account he was by far the elder of the two (he said that he remembered the first acorn, so by definition he must have been older than even the oldest of the Ents).

Tom Bombadil was a mysterious magical being or spirit, whereas Treebeard was a living creature created in the distant past as a protector of the trees of Middle-earth. He did not in fact awaken until soon after the first Elves, but at the end of the Third Age, he may well have been the oldest living being in the mortal world. As such, when Celeborn addressed him as 'Eldest', that title seems to have been quite appropriate.

Tom's origins are clouded in mystery, but from his own account he was extraordinarily old. He seems to have been in the World even before the Valar entered it, which would make him the oldest being of any kind to inhabit Arda at the end of the Third Age (assuming, of course, that there weren't others of his mysterious kind elsewhere in the World).

Treebeard was the eldest of the Ents, and that race of beings dated back into the ancient history of Arda; according to legend, they were created to counteract the Dwarves' need for wood, and appeared after the first Elves and Dwarves, but before Men had awakened. Treebeard was therefore exceptionally old, dating back to the dim origins of the World, but even he was not so old as Tom Bombadil, who had apparently been within Arda since its first days.